Human hair usually emerges from the scalp in groups of 2 or 3-hair units. Hair densities and grouping patterns in androgenetic alopecia (AGA) patients are known to be different from those in normal adults, but no comparative study has ever before been made in Korea. Therefore we have developed some technical improvements on phototrichogram methodology to evaluate the differences between these two groups.

Objectives: This study was performed to quantify Koreans' hair characteristics at each site (vertex, occipital, temporal) of the scalp according to the age and to compare the differences of hair characteristics of AGA and normal adults using phototrichogram.

Hairs in the precisely defined circle at each (vertex, temporal, occipital) site of the scalp in 37 AGA male patients and 15 healthy male volunteers were evaluated according to age. Each circumscribed area of the scalp, centered with a dot tattoo to ensure reproducibility, was photographed just after shaving, and named 'primary image'. Two days later, the same area was again photographed, and named 'secondary image', from which the hair density and the grouping pattern of hair follicular units were determined by the image analyzer program.

The results can be summarized as follows:

1. In normal adult males, the range of hair density was 117±13/cm²~140±16/cm², with the hair density of the occiput being significantly higher than that of the temple. No significant differences in hair density were shown between vertex and occiput.

2. In AGA male patients, the range of hair density was 102±23/cm²-137±17/cm², and the differences of the hair density between vertex and occiput were statistically significant.

3. The numbers of grouped hair units per square centimeter in the non-bald adult male group ranged from 59±11/cm² to 73±14/cm². The most common grouped hair unit was a 2-hair unit, followed by a 1-hair unit and a 3-hair unit group.

4. In the AGA group, the numbers of grouped hair units per square centimeter ranged from 57±6/cm² to 72±12/cm², showing no significance with the control group. The most common grouped hair unit was a 1-hair unit, followed by a 2-hair unit and a 3-hair unit group.

The AGA group compared remarkably with the normal adult male group, showing a lower hair density with a larger proportion of 1-grouped hair units. Based on the data about hair density and hair grouping patterns in AGA patients, surgeons can estimate the area of donor scalp with the most probable number of follicular units in hair trans-plantation procedures.